This invention relates to polymer coatings, such as pigmented paints and clear overprint varnishes. It further relates to letdown vehicles used in aqueous flexographic inks and to partial or sole vehicles used in gravure and general ink formulations. Additionally it relates to polymer coatings for leather or leather substitutes, especially those applied to serve as an embossing release coat and a final topcoat, and to improved floor polishes and cement compositions.
In the field of paints and varnishes, as well as in the field of floor finishes and inks, mixtures or blends of alkali-soluble polymers with alkali-insoluble polymers have been utilized for many years. The alkali- soluble polymers are generally prepared by solution polymerization, although they can also be prepared by emulsion or dispersion polymerization techniques. U.S. Pat. No. 3,037,952 is typical of this technology.
European Patent Application Publication No. 0207854 Al discloses a storage-stable coating composition containing core-shell polymer particles containing (A) 95-99% by weight of at least one C.sub.1 --C.sub.8 alkyl acrylate or methacrylate and (B) 1-5% by weight of at least one watersoluble monomer.
While said prior art systems are quite useful and commercially successful, improvements in the area of water resistance, heat seal resistance, block resistance, rheology, stability and efficiency in preparation have been desired. The prior systems generally could not be prepared with more than about 35% by weight alkali-soluble polymer, whereas it has been desired to prepare up to 60% by weight alkali-soluble polymer.
In the printing ink field letdown vehicles have been used commercially in pigment dispersions for flexographic inks for some time. Such dispersions are usually prepared in emulsion and are high in styrene content. They are added to adjust viscosity, give the ink proper rheology, and aid in dry time, resistance properties, and film formation of the final dried ink formulation. The pigment dispersions generally comprise solvent- or emulsion-based resins of low molecular weight and high acid content. Many process and stability problems have been experienced with these dispersions which can be eliminated by the use of the core-shell polymers of the present invention.
Acrylic and modified-acrylic latex polymers containing copolymerized acid groups, often treated with zinc or other ions, are well known as components of floor polish vehicles. U.S. Pat. Nos. 3,328,325 and 4,517,330 disclose such floor polishes containing acrylic polymers. The core-shell polymers of this invention are useful in the floor polish applications and exhibit better gloss performance than the acrylic-containing floor polishes known in the prior art.
In the field of leather embossing coatings, nitrocellulose lacquer emulsions have traditionally been used for many years. Although these lacquer systems are commercially useful, improvements in the areas of product stability, application rheology, gloss, fill, lower organic solvent content and non-flammability are desired. Water-based coatings containing the core-shell polymers of this invention give advantages in all these areas.
It is an object of the present invention to provide core-shell polymers and compositions thereof which exhibit good rheology and ease of application and which are stable, water resistant, heat-seal resistant, and efficiently prepared by a process which permits levels of alkali-soluble polymer up to about 60% by weight. It is a further object to provide core-shell polymers which can be readily and inexpensively isolated from emulsion and utilized in improved cement formulations. It is also a further object of this invention to provide core-shell polymers and compositions thereof which are useful in various applications, such as inks, varnishes, paints and other interior or exterior architectural coatings, leather coatings, cement compositions and floor polishes by virtue of their improved gloss, high temperature modulus, and other superior properties.
These objects, and others as will become apparent from the following description, are achieved by the present invention which comprises in part a composition comprising a core-shell polymer having an alkali-insoluble, emulsion polymer core and an alkali-soluble, emulsion polymer shell attached or associated with said core so that, upon dissolving said shell with alkali, a small portion of said shell remains attached or associated with said core.